I can confirm that feature 'Use SMTP To Send E-mail' is unusable currently (v. 3.0.6).

Mails cause bans with error like the following:

status=bounced (host gmail-smtp-in.l.google.com[64.233.162.26] said: 550-5.7.1 [188.120.250.223 11] Our system has detected that this message is 550-5.7.1 not RFC 5322 compliant. To reduce the amount of spam sent to Gmail, 550-5.7.1 this message has been blocked. Please review 550 5.7.1 RFC 5322 specifications for more information. l73si6051874lfg.249 - gsmtp (in reply to end of DATA command))